Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoding method is provided for encoding a picture to generate a coded stream. The encoding method incldues: generating a first prediction image of a current block included in a current picture by referring to a first region included in a reference picture different from the current picture; operating a bi-directional optical flow process to generate a second prediction image based on the first prediction image by referring to a second region included in the first region, and not operating the bi-directional optical flow process by referring to a third region not included in the first region; and encoding the current block based on the second prediction image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of Ser. No.16/860,367, filed Apr. 28, 2020, which is a U.S. continuationapplication of PCT International Patent Application NumberPCT/JP2018/039421 filed on Oct. 24, 2018, claiming the benefit ofpriority of U.S. Provisional Patent Application No. 62/578756 filed onOct. 30, 2017, the entire contents of which are hereby incorporated byreference.

BACKGROUND 1. Technical Field

The present disclosure relates to an encoder, a decoder, an encodingmethod, and a decoding method.

2. Description of the Related Art

The video coding standard called High-Efficiency Video Coding (HEVC) isstandardized by the Joint Collaborative Team on Video Coding (JCT-VC).

SUMMARY

An encoder according to an aspect of the present disclosure is anencoder that encodes a picture to generate a coded stream includes:circuitry and a memory coupled to the circuitry. The circuitry performs,using the memory: generating a prediction image of a current blockincluded in a current picture by referring to a first region included ina reference picture different from the current picture; operating abi-directional optical flow process to correct the prediction image byreferring to a second region included in the first region, and notoperating the bi-directional optical flow process in response to thesecond region not being included in the first region; and encoding thecurrent block based on the prediction image.

A decoder according to an aspect of the present disclosure is a decoderthat decodes a coded stream to generate a picture includes: circuitry;and a memory coupled to the circuitry, wherein the circuitry performs,using the memory: generating a prediction image of a current blockincluded in a current picture by referring to a first region included ina reference picture different from the current picture; operating abi-directional optical flow process to correct the prediction image byreferring to a second region included in the first region, and notoperating the bi-directional optical flow process in response to thesecond region not being included in the first region; and decoding thecurrent block based on the prediction image.

Note that these general and specific aspects may be implemented using asystem, a method, an integrated circuit, a computer program, acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs or recordingmedia.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1;

FIG. 2 illustrates one example of block splitting according toEmbodiment 1;

FIG. 3 is a chart indicating transform basis functions for eachtransform type;

FIG. 4A illustrates one example of a filter shape used in ALF;

FIG. 4B illustrates another example of a filter shape used in ALF;

FIG. 4C illustrates another example of a filter shape used in ALF;

FIG. 5A illustrates 67 intra prediction modes used in intra prediction;

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing;

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing;

FIG. 5D illustrates one example of FRUC;

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory;

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture;

FIG. 8 is for illustrating a model assuming uniform linear motion;

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks;

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode;

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing;

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing;

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1;

FIG. 11 is a block diagram illustrating an internal configuration of aninter predictor of the encoder according to Embodiment 1;

FIG. 12 illustrates examples of positions of motion estimation regioninformation in bitstreams in Embodiment 1;

FIG. 13 is a flowchart illustrating processing performed by interpredictors of the encoder and the decoder according to Embodiment 1;

FIG. 14 illustrates an example of a candidate list in Embodiment 1;

FIG. 15 illustrates an example of a reference picture list in Embodiment1;

FIG. 16 illustrates an example of a motion estimation region inEmbodiment 1;

FIG. 17 illustrates an example of an adjacent region in Embodiment 1;

FIG. 18 is a block diagram illustrating an internal configuration of theinter predictor of the decoder according to Embodiment 1;

FIG. 19 illustrates an example of a motion estimation region inVariation 2 of Embodiment 1;

FIG. 20 illustrates an example of a motion estimation region inVariation 4 of Embodiment 1;

FIG. 21 illustrates an example of a motion estimation region inVariation 5 of Embodiment 1;

FIG. 22 illustrates an example of a motion estimation region inVariation 6 of Embodiment 1;

FIG. 23 is a block diagram illustrating a functional configuration of anencoding and decoding system according to Variation 7 of Embodiment 1;

FIG. 24 illustrates motion estimation regions in Variation 9 of

Embodiment 1;

FIG. 25 is a block diagram illustrating an internal configuration of aninter predictor of an encoder and a decoder according to Variation 10 ofEmbodiment 1;

FIG. 26 is a flow chart illustrating processing performed by the interpredictor of the encoder and the decoder according to Variation 10 ofEmbodiment 1;

FIG. 27 illustrates an overall configuration of a content providingsystem for implementing a content distribution service;

FIG. 28 illustrates one example of an encoding structure in scalableencoding;

FIG. 29 illustrates one example of an encoding structure in scalableencoding;

FIG. 30 illustrates an example of a display screen of a web page;

FIG. 31 illustrates an example of a display screen of a web page;

FIG. 32 illustrates one example of a smartphone; and

FIG. 33 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(Underlying Knowledge Forming Basis of the Present Disclosure)

Furthermore, a mode in which a motion vector or a motion compensatedimage to be estimated in this manner is corrected is also beingconsidered for a next-generation video compression standard. Even forsuch a mode, there is a demand for technology of inhibiting increases inprocessing load and memory bandwidth.

In view of this, an encoder according to an aspect of the presentdisclosure is an encoder that encodes a current block using a motionvector, and includes: circuitry; and a memory, wherein the circuitry,using the memory: estimates a motion vector of the current block withoutusing an image of the current block by referring to a first regioninside a reference picture, and performs motion compensation using theestimated motion vector; identifies a second region inside the referencepicture, the second region being referred to in a correction process ofcorrecting a prediction image of the current block obtained using theestimated motion vector or via the motion compensation; and permits thecorrection process when the second region is entirely included in thefirst region, and prohibits the correction process when the secondregion is not entirely included in the first region.

According to this, there is no need to refer to a new region followingthe correction process, and thus a new reference image need not be readfrom the frame memory, and the required amount of memory bandwidth forthe correction process can be reduced.

An encoding method according to an aspect of the present disclosure isan encoding method of encoding a current block using a motion vector,and includes: estimating a motion vector of the current block withoutusing an image of the current block by referring to a first regioninside a reference picture, and performing motion compensation using theestimated motion vector; identifying a second region inside thereference picture, the second region being referred to in a correctionprocess of correcting a prediction image of the current block obtainedusing the estimated motion vector or via the motion compensation; andpermitting the correction process when the second region is entirelyincluded in the first region, and prohibiting the correction processwhen the second region is not entirely included in the first region.

According to this, advantageous effects similar to those yielded byencoder described above can be produced.

A decoder according to an aspect of the present disclosure is a decoderthat decodes a current block using a motion vector, and includes:circuitry; and a memory, wherein the circuitry, using the memory:estimates a motion vector of the current block without using an image ofthe current block by referring to a first region inside a referencepicture, and performs motion compensation using the estimated motionvector; identifies a second region inside the reference picture, thesecond region being referred to in a correction process of correcting aprediction image of the current block obtained using the estimatedmotion vector or via the motion compensation; and permits the correctionprocess when the second region is entirely included in the first region,and prohibits the correction process when the second region is notentirely included in the first region.

According to this, there is no need to refer to a new region followingthe correction process, and thus a new reference image need not be readfrom the frame memory, and the required amount of memory bandwidth forthe correction process can be reduced.

A decoding method according to an aspect of the present disclosure is adecoding method of decoding a current block using a motion vector, andincludes: estimating a motion vector of the current block without usingan image of the current block by referring to a first region inside areference picture, and performing motion compensation using theestimated motion vector; identifying a second region inside thereference picture, the second region being referred to in a correctionprocess of correcting a prediction image of the current block obtainedusing the estimated motion vector or via the motion compensation; andpermitting the correction process when the second region is entirelyincluded in the first region, and prohibiting the correction processwhen the second region is not entirely included in the first region.

According to this, advantageous effects similar to those yielded by thedecoder described above can be produced.

Note that these general and specific aspects may be implemented using asystem, an integrated circuit, a computer program, a computer-readablerecording medium such as a CD-ROM, or any combination of systems,integrated circuits, computer programs or recording media.

Hereinafter, embodiments will be described with reference to thedrawings.

Note that the embodiments described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc., indicated in the following embodiments are mere examples,and therefore are not intended to limit the scope of the claims.Therefore, among the components in the following embodiments, those notrecited in any of the independent claims defining the broadest inventiveconcepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) _(co)mbining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) _(co)mbining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1 , encoder 100 is a device that encodes apicture block by block, and includes splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, block memory 118, loop filter120, frame memory 122, intra predictor 124, inter predictor 126, andprediction controller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2 , the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×Γblocks (binary tree block splitting). As a result, thetop left 64×64 block is split into two 16×Γblocks 11 and 12 and one32×64 block 13. The top right 64×64 block is horizontally split into tworectangle 64×32 blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2 , block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2 , one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3 , N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see 11.265 (ISO/IEC23008-2 HEVC (High Efficiency Video Coding))).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L. Similarly, aprediction image (Pred_U) is obtained by applying a motion vector (MV_U)of the encoded neighboring upper block to the current block, and asecond pass of the correction of the prediction image is made bysuperimposing the prediction image resulting from the first pass andPred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6 , in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7 , in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8 , (v_(x), v_(y)) denotes a velocity vector, and τ₀ and denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MV_(y0)) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.MATH. 1∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) /I ^((k))/∂y=0.   (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

MATH.  2 $\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10 , decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[Internal Configuration of Inter Predictor of Encoder]

Next, the internal configuration of inter predictor 126 of encoder 100is to be described. Specifically, the functional configuration of interpredictor 126 of encoder 100 that allows the decoder to carry out a modefor motion estimation (the FRUC mode) is to be described.

FIG. 11 is a block diagram illustrating the internal configuration ofinter predictor 126 of encoder 100 according to Embodiment 1. Interpredictor 126 includes candidate derivator 1261, region determiner 1262,motion estimator 1263, and motion compensator 1264.

Candidate derivator 1261 derives a plurality of candidates each havingat least one motion vector. The candidates may be referred to as motionvector predictor candidates. The motion vectors that the candidates havemay be referred to as motion vector predictors.

Specifically, candidate derivator 1261 derives a plurality ofcandidates, based on motion vectors of encoded blocks that spatially ortemporally neighbor a current block (hereinafter, referred to asneighboring blocks). A motion vector of a neighboring block is a motionvector used for compensating motion of the neighboring block.

For example, when two reference pictures are referred to during interprediction for one neighboring block, candidate derivator 1261 derivesone candidate having two reference picture indexes and two motionvectors, based on two motion vectors corresponding to the two referencepictures. For example, when one reference picture is referred to duringinter prediction for one neighboring block, candidate derivator 1261derives one candidate having one reference picture index and one motionvector, based on one motion vector corresponding to the one referencepicture.

A plurality of candidates derived from a plurality of neighboring blocksare registered in the candidate list. At this time, a redundantcandidate may be eliminated from the candidate list. A candidate havinga motion vector (for example, a zero motion vector) with a fixed valuemay be registered if the candidate list is not filled with candidates.Note that the candidate list may be in common with the merge list usedin the merge mode.

A spatially neighboring block means a block included in the currentpicture and neighboring the current block. A spatially neighboring blockis, for example, a block on the left, the upper left, the top, or theupper right of the current block. A motion vector derived from aspatially neighboring block may be referred to as a spatial motionvector.

A temporally neighboring block means a block included in anencode/decoded picture different from the current picture. The positionof a temporally neighboring block in an encoded/decoded picturecorresponds to the position of the current block in the current picture.A temporally neighboring block may be referred to as a co-located block.A motion vector derived from a temporally neighboring block may bereferred to as a temporal motion vector.

Region determiner 1262 determines a motion estimation region in areference picture. The motion estimation region means a partial regionin the reference picture, in which motion estimation is allowed.

The size of the motion estimation region is determined based on a memorybandwidth and a throughput, for example. The memory bandwidth and thethroughput can be obtained from the levels defined according to thestandard, for example. The memory bandwidth and the throughput may beobtained from a decoder. The size of the motion estimation region meansthe size of a partial region in a picture, and can be represented by,for example, the horizontal pixel count and the vertical pixel countthat indicate the distances from the center of the motion estimationregion to a vertical side and a horizontal side, respectively.

The position of the motion estimation region is determined based on astatistical representative vector of a plurality of motion vectors thata plurality of candidates in the candidate list have, for example. Inthe present embodiment, an average motion vector is used as astatistical representative vector. An average motion vector is made upof an average of horizontal values and an average of vertical values ofa plurality of motion vectors.

Information on the determined motion estimation region (hereinafter,referred to as motion estimation region information) is encoded in abitstream. Motion estimation region information includes at least one ofinformation indicating the size of the motion estimation region orinformation indicating the position of the motion estimation region, andincludes only information indicating the size of the motion estimationregion in the present embodiment. The position of motion estimationregion information in a bitstream is not limited in particular. Forexample, motion estimation region information may be written in, asillustrated in FIG. 12 , (i) a video parameter set (VPS), (ii) asequence parameter set (SPS), (iii) a picture parameter set (PPS), (iv)a slice header, or (v) a video system setting parameter. Note thatmotion estimation region information may be or may not be subjected toentropy encoding.

Motion estimator 1263 performs motion estimation within the motionestimation region in a reference picture. Specifically, motion estimator1263 performs motion estimation in only the motion estimation region inthe reference picture. Specifically, motion estimator 1263 performsmotion estimation as follows.

First, motion estimator 1263 reads a reconstructed image of the motionestimation region in the reference picture from frame memory 122. Forexample, motion estimator 1263 reads only a reconstructed image of themotion estimation region within the reference picture. Then, motionestimator 1263 excludes a candidate having a motion vector correspondingto the position outside the motion estimation region in the referencepicture, from a plurality of candidates derived by candidate derivator1261. Stated differently, motion estimator 1263 eliminates a candidatehaving a motion vector pointing to a position outside the motionestimation region from the candidate list.

Next, motion estimator 1263 selects a candidate from among the one ormore remaining candidates. Thus, motion estimator 1263 selects acandidate from the candidate list from which a candidate having a motionvector corresponding to the position outside the motion estimationregion has been eliminated.

Such candidate selection is based on evaluation values of thecandidates. For example, when first pattern matching (bilateralmatching) described above is applied, the evaluation value of eachcandidate is calculated based on a difference value between areconstructed image of a region in the reference picture correspondingto a motion vector of the candidate and a reconstructed image of aregion in another reference picture on the motion trajectory of thecurrent block. Furthermore, for example, when second pattern matching(template matching) is applied, the evaluation value of each candidateis calculated based on a difference value between a reconstructed imageof a region in a reference picture corresponding to a motion vector ofthe candidate and a reconstructed image of an encoded block neighboringthe current block in a current picture.

Finally, motion estimator 1263 determines a motion vector for thecurrent block, based on the selected candidate. Specifically, motionestimator 1263 performs, for example, pattern matching in an adjacentregion included in the reference picture and corresponding to the motionvector that the selected candidate has, to search for a matching regionfor the current block in the adjacent region. Motion estimator 1263determines a motion vector for the current block based on the matchingregion in the adjacent region. For example, motion estimator 1263 maydetermine the motion vector that the selected candidate has, as themotion vector for the current block.

Motion compensator 1264 performs motion compensation using the motionvector determined by motion estimator 1263, to generate an interprediction signal for the current block.

[Operation of Inter Predictor of Encoder]

Next, operation of inter predictor 126 configured as above is to bedescribed in detail with reference to FIGS. 13 to 17 . The followingdescribes the case where inter prediction is performed with reference toa single reference picture.

FIG. 13 is a flowchart illustrating processing performed by the interpredictors of the encoder and the decoder according to Embodiment 1. InFIG. 13 , the numeral in the parentheses denotes processing performed bythe inter predictor of the decoder.

First, candidate derivator 1261 derives a plurality of candidates fromneighboring blocks, and generates a candidate list (S101). FIG. 14illustrates an example of the candidate list in Embodiment 1. Here, thecandidates each have a candidate index, a reference picture index, and amotion vector.

Next, region determiner 1262 selects a reference picture from thereference picture list (S102). For example, region determiner 1262selects a reference picture in ascending order of the reference pictureindexes. For example, in the reference picture list in FIG. 15 , regiondeterminer 1262 first selects a reference picture having a referencepicture index “0”.

Region determiner 1262 determines a motion estimation region in thereference picture (S103). Here, the determination of the motionestimation region is to be described, with reference to FIG. 16 .

FIG. 16 illustrates an example of motion estimation region 1022 inEmbodiment 1. FIG. 16 illustrates current block 1000 and neighboringblocks 1001 to 1004 in a current picture, in the corresponding positionsin a reference picture.

First, region determiner 1262 obtains motion vectors 1011 to 1014 ofneighboring blocks 1001 to 1004 from the candidate list. Regiondeterminer 1262 scales motion vectors 1011 to 1014 if necessary, andcalculates average motion vector 1020 of motion vectors 1011 to 1014.

For example, region determiner 1262 calculates an average of thehorizontal values of motion vectors “−25(=((−48)+(−32)+0+(−20))/4)” andan average of the vertical values of motion vectors “6 (=(0+9+12+3)/4)”,to calculate an average motion vector (−26, 6), with reference to thecandidate list in FIG. 14 .

Next, region determiner 1262 determines representative position 1021 ofthe motion estimation region, based on average motion vector 1020. Thecenter position is adopted as representative position 1021, here. Notethat representative position 1021 is not limited to the center position,and one of the vertex positions of the motion estimation region (forexample, the upper left vertex position) may be used.

Further, region determiner 1262 determines the size of the motionestimation region, based on the memory bandwidth and the throughput, forinstance. For example, region determiner 1262 determines the horizontalpixel count and the vertical pixel count that indicate the size of themotion estimation region.

Based on representative position 1021 and the size of the motionestimation region that are determined in this manner, region determiner1262 determines motion estimation region 1022.

Here, the description returns to the flowchart in FIG. 13 . Motionestimator 1263 excludes a candidate having a motion vector correspondingto the position outside the motion estimation region from the candidatelist (S104). For example, in FIG. 16 , motion estimator 1263 excludescandidates having motion vectors 1012 and 1013 pointing to the positionsoutside the motion estimation region from the candidate list.

Motion estimator 1263 calculates evaluation values of candidatesremaining in the candidate list (S105). For example, motion estimator1263 calculates, as an evaluation value, a difference value between areconstructed image (template) of a neighboring block in the currentpicture and a reconstructed image of a region in the reference picturecorresponding to a motion vector of a candidate (template matching). Inthis case, a region in the reference picture corresponding to a motionvector of a candidate is a region of a neighboring block that has beensubjected to motion compensation using the motion vector of thecandidate in the reference picture. The smaller the evaluation valuecalculated in this manner is, the higher the evaluation is. Note that anevaluation value may be a reciprocal of a difference value. In thiscase, the greater the evaluation value is, the higher the evaluation is.

Motion estimator 1263 selects a candidate from the candidate list, basedon the evaluation values (S106). For example, motion estimator 1263selects a candidate having the smallest evaluation value.

Motion estimator 1263 determines an adjacent region corresponding to themotion vector that the selected candidate has (S107). For example, whenmotion vector 1014 in FIG. 16 is selected, motion estimator 1263determines, in the reference picture, adjacent region 1023 of thecurrent block that has been subjected to motion compensation usingmotion vector 1014, as illustrated in FIG. 17 .

The size of adjacent region 1023 may be defined by a standard inadvance, for example. Specifically, for example, fixed sizes such as the8×8, 16×16, or 32×32 pixel size may be defined as the size of adjacentregion 1023, in advance. The size of adjacent region 1023 may bedetermined based on the throughput. In this case, information on thesize of adjacent region 1023 may be written in a bitstream. Thehorizontal pixel count and the vertical pixel count that indicate thesize of the motion estimation region may be determined and written in abitstream, taking into consideration of the size of adjacent region1023.

Motion estimator 1263 determines whether the determined adjacent regionis entirely included in the motion estimation region (S108).Specifically, motion estimator 1263 determines whether the entireadjacent region is included in the motion estimation region.

Here, if the adjacent region is entirely included in the motionestimation region (Yes in S108), motion estimator 1263 performs patternmatching in the adjacent region (S109). As a result, motion estimator1263 obtains an evaluation value of a region in the reference picturewhich matches a reconstructed image of a neighboring block in theadjacent region.

On the other hand, when the adjacent region is not entirely included inthe motion estimation region (No in S108), motion estimator 1263performs pattern matching in a partial region of the adjacent regionincluded in the motion estimation region (5110). Specifically, motionestimator 1263 does not perform pattern matching in a partial region ofthe adjacent region not included in the motion estimation region.

Region determiner 1262 determines whether the reference picture includesan unselected reference picture (S111). Here, when there is anunselected reference picture (Yes in S111), the processing returns tothe selection of a reference picture (S102).

On the other hand, when there is no unselected reference picture (No inS111), motion estimator 1263 determines a motion vector for the currentpicture, based on evaluation values (S112). Specifically, motionestimator 1263 determines a motion vector of the most highly evaluatedcandidate among a plurality of reference pictures, as the motion vectorfor the current picture.

[Internal Configuration of Inter Predictor of Decoder]

Next, the internal configuration of inter predictor 218 of decoder 200is to be described. Specifically, the functional configuration of interpredictor 218 of decoder 200 that allows the decoder to carry out a modefor motion estimation (the FRUC mode) is to be described.

FIG. 18 is a block diagram illustrating the internal configuration ofinter predictor 218 of decoder 200 according to Embodiment 1. Interpredictor 218 includes candidate derivator 2181, region determiner 2182,motion estimator 2183, and motion compensator 2184.

Candidate derivator 2181 derives a plurality of candidates each havingat least one motion vector, similarly to candidate derivator 1261 ofencoder 100. Specifically, candidate derivator 2181 derives a pluralityof candidates, based on motion vectors of temporally and/or spatiallyneighboring blocks.

Region determiner 2182 determines the motion estimation region in areference picture. Specifically, region determiner 2182 first obtainsmotion estimation region information parsed from a bitstream. Then,region determiner 2182 determines the size of the motion estimationregion, based on the motion estimation region information. Furthermore,region determiner 2182 determines the position of the motion estimationregion similarly to region determiner 1262 of encoder 100. Accordingly,the motion estimation region in the reference picture is determined.

Motion estimator 2183 performs motion estimation within the motionestimation region in the reference picture. Specifically, motionestimator 2183 first reads, from frame memory 214, a reconstructed imageof the motion estimation region in the reference picture. For example,motion estimator 2183 reads only the reconstructed image of the motionestimation region within the reference picture. Motion estimator 2183performs motion estimation within the motion estimation region, anddetermines a motion vector for the current block, similarly to motionestimator 1263 of encoder 100.

Motion compensator 2184 performs motion compensation using the motionvector determined by motion estimator 2183, to generate an interprediction signal for the current block.

[Operation of Inter Predictor of Decoder]

Next, operation of inter predictor 218 having the configuration asdescribed above is to be described with reference to FIG. 13 . Theprocessing by inter predictor 218 is the same as the processing by interpredictor 126 of encoder 100, except that step S103 is replaced withstep S203. The following describes step S203.

Region determiner 2182 determines the motion estimation region in thereference picture (S203). At this time, region determiner 2182determines the size of the motion estimation region, based on the motionestimation region information parsed from the bitstream. Furthermore,region determiner 2182 determines the position of the motion estimationregion, based on a plurality of candidates included in a candidate list,similarly to region determiner 1262 of encoder 100.

[Advantageous Effects and Others]

As described above, inter predictor 126 of encoder 100 and interpredictor 218 of decoder 200 according to the present embodiment canexclude a candidate having a motion vector corresponding to the positionoutside the motion estimation region, and thereafter can select acandidate. Accordingly, the processing load for selecting a candidatecan be reduced. Further, it is not necessary to read a reconstructedimage of a region outside the motion estimation region from the framememory, and thus the memory bandwidth for motion estimation can bereduced.

According to encoder 100 and decoder 200 according to the presentembodiment, information on the motion estimation region can be writtenin a bitstream, and the bitstream can be parsed from the information onthe motion estimation region. Accordingly, decoder 200 can also use thesame motion estimation region as the motion estimation region used byencoder 100. Furthermore, the processing load on decoder 200 fordetermining the motion estimation region can be reduced.

According to encoder 100 and decoder 200 according to the presentembodiment, information indicating the size of the motion estimationregion can be included in a bitstream. Accordingly, decoder 200 can alsouse the motion estimation region having the same size as the size of themotion estimation region used by encoder 100. Further, the processingload on decoder 200 for determining the size of the motion estimationregion can be reduced.

According to inter predictor 126 of encoder 100 and inter predictor 218of decoder 200 according to the present embodiment can determine theposition of the motion estimation region, based on an average motionvector obtained from a plurality of candidates derived from a pluralityof blocks neighboring the current block. Accordingly, a region suitablefor the search of a motion vector for the current block can bedetermined as the motion estimation region, and the accuracy of themotion vector can be improved.

According to inter predictor 126 of encoder 100 and inter predictor 218of decoder 200 according to the present embodiment, a motion vector forthe current block can be determined based on pattern matching in anadjacent region, in addition to a motion vector of a candidate.Accordingly, the accuracy of the motion vector can be further improved.

According to inter predictor 126 of encoder 100 and inter predictor 218of decoder 200 according to the present embodiment, when an adjacentregion is not included in the motion estimation region, pattern matchingcan be performed in a partial region of the adjacent region included inthe motion estimation region. Accordingly, motion estimation in a regionoutside the motion estimation region can be avoided, and processing loadand the required amount of the memory bandwidth can be reduced.

Variation 1 of Embodiment 1

In Embodiment 1 above, the position of the motion estimation region isdetermined based on an average motion vector of motion vectors that aplurality of candidates in the candidate list have, whereas in thisvariation, the position of the motion estimation region is determinedbased on a median motion vector of a plurality of motion vectors that aplurality of candidates in the candidate list have.

Region determiners 1262 and 2182 according to this variation obtain aplurality of motion vectors that a plurality of candidates have, withreference to the candidate list. Region determiners 1262 and 2182calculate the median motion vector of the obtained motion vectors. Themedian motion vector is a motion vector constituted by a median of thehorizontal values of the motion vectors and a median of the verticalvalues of the motion vectors.

Region determiners 1262 and 2182 calculate, with reference to, forexample, the candidate list in FIG. 14 , the median“−26(=((−32)+(−20))/2)” of the horizontal values of the motion vectorsand the median of vertical values “6(=(9+3)/2)”, to calculate medianmotion vector (−26, 6).

Next, region determiners 1262 and 2182 determine the representativeposition of a motion estimation region, based on the calculated medianmotion vector.

As described above, region determiners 1262 and 2182 according to thisvariation can determine the position of the motion estimation region,based on the median motion vector obtained from a plurality ofcandidates derived from a plurality of blocks neighboring the currentblock. Accordingly, a region suitable for the search of a motion vectorfor the current block can be determined as the motion estimation region,and the accuracy of the motion vector can be improved.

Variation 2 of Embodiment 1

Next, Variation 2 of Embodiment 1 is to be described. In this variation,the position of the motion estimation region is determined based on thesmallest motion vector, instead of an average motion vector. Thefollowing describes this variation, focusing on a different point fromEmbodiment 1 above.

Region determiners 1262 and 2182 according to this variation obtain aplurality of motion vectors that a plurality of candidates have, withreference to the candidate list. Region determiners 1262 and 2182 selecta motion vector (specifically, the smallest motion vector) that has thesmallest magnitude, from among the obtained motion vectors.

Region determiners 1262 and 2182 select the motion vector (0, 8) thatthe candidate with the candidate index “2” has and has the smallestmagnitude from among the plurality of motion vectors, with reference tothe candidate list in FIG. 14 , for example.

Next, region determiners 1262 and 2182 determine the representativeposition of the motion estimation region, based on the selected smallestmotion vector.

FIG. 19 illustrates an example of the motion estimation region inVariation 2 of Embodiment 1. In FIG. 19 , region determiners 1262 and2182 select motion vector 1013 that has the smallest magnitude amongmotion vectors 1011 to 1014 of neighboring blocks as smallest motionvector 1030. Next, region determiners 1262 and 2182 determinerepresentative position 1031 of the motion estimation region, based onsmallest motion vector 1030. Then, region determiners 1262 and 2182determine motion estimation region 1032, based on determinedrepresentative position 1031.

As described above, region determiners 1262 and 2182 according to thisvariation can determine the position of the motion estimation region,based on the smallest motion vector obtained from candidates derivedfrom blocks neighboring the current block. Accordingly, the region closeto a current block can be determined as the motion estimation region,and the accuracy of a motion vector can be improved.

Variation 3 of Embodiment 1

Next, Variation 3 of Embodiment 1 is to be described. In this variation,the position of a motion estimation region is determined based on amotion vector of an encoded/decoded picture different from the currentpicture, instead of an average motion vector. The following is todescribe this variation, focusing on a different point from Embodiment 1above.

Region determiners 1262 and 2182 according to this variation select areference picture that is an encoded/decoded picture different from thecurrent picture, with reference to the reference picture list. Forexample, region determiners 1262 and 2182 select a reference picturehaving a reference picture index of the smallest value. For example,region determiners 1262 and 2182 may select a reference picture closestto the current picture in the output order.

Next, region determiners 1262 and 2182 obtain a plurality of motionvectors that have been used to encode/decode a plurality of blocksincluded in the selected reference picture. Region determiners 1262 and2182 calculate an average motion vector of the obtained motion vectors.

Then, region determiners 1262 and 2182 determine the representativeposition of the motion estimation region, based on the calculatedaverage motion vector.

As described above, according to region determiners 1262 and 2182according to this variation, even when the current block in a currentpicture is changed, the motion vector of an encoded/decoded picture doesnot change, and thus it is unnecessary to determine a motion estimationregion from the motion vectors of neighboring blocks each time thecurrent block is changed. Specifically, the processing load fordetermining a motion estimation region can be reduced.

Note that here, although the representative position of the motionestimation region is determined based on the average motion vector ofthe selected reference picture, the present disclosure is not limited tothis. For example, a median motion vector may be used instead of anaverage motion vector. For example, the motion vector of a co-locatedblock may be used instead of an average motion vector.

Variation 4 of Embodiment 1

Next, Variation 4 of Embodiment 1 is to be described. In this variation,a reference picture is split into a plurality of regions, and motionvectors that candidates have are groped based on the split regions. Atthis time, the position of the motion estimation region is determinedbased on a group that includes the greatest number of motion vectors.

The following describes this variation, focusing on a different pointfrom Embodiment 1 above, with reference to FIG. 20 . FIG. 20 illustratesan example of the motion estimation region in Variation 4 of Embodiment1.

Region determiners 1262 and 2182 according to this variation split areference picture into regions. For example, as illustrated in FIG. 20 ,region determiners 1262 and 2182 split a reference picture into fourregions (first to fourth regions), based on the position of a currentpicture.

Region determiners 1262 and 2182 group motion vectors of neighboringblocks, based on the regions. For example, in FIG. 20 , regiondeterminers 1262 and 2182 group motion vectors 1011 to 1014 into a firstgroup that includes motion vector 1013 corresponding to the firstregion, and a second group that includes motion vectors 1011, 1012, and1014 corresponding to the second region.

Region determiners 1262 and 2182 determine the position of a motionestimation region, based on a group that includes the greatest number ofmotion vectors. For example, in FIG. 20 , region determiners 1262 and2182 determine representative position 1041 of the motion estimationregion, based on average motion vector 1040 of motion vectors 1011,1012, and 1014 included in the second group. Note that a median motionvector or the smallest motion vector may be used instead of an averagemotion vector.

As described above, region determiners 1262 and 2182 according to thisvariation can determine a region suitable for the search of a motionvector for a current block as the motion estimation region, and thus theaccuracy of the motion vector can be improved.

Variation 5 of Embodiment 1

Next, Variation 5 of Embodiment 1 is to be described. The position of amotion estimation region is corrected in this variation, which differsfrom Embodiment 1 above. The following describes this variation,focusing on a different point from Embodiment 1 above with reference toFIG. 21 . FIG. 21 illustrates an example of the motion estimation regionin Variation 5 of Embodiment 1.

Region determiners 1262 and 2182 according to this variation correct theposition of the motion estimation region determined based on the averagemotion vector, for example. Specifically, first, region determiners 1262and 2182 temporarily determine a motion estimation region, based on theaverage motion vector of a plurality of motion vectors that a pluralityof candidates have. For example, region determiners 1262 and 2182temporarily determine motion estimation region 1050, as illustrated inFIG. 21 .

Here, region determiners 1262 and 2182 determine whether the positioncorresponding to a zero motion vector is included in the motionestimation region temporarily determined. Specifically, regiondeterminers 1262 and 2182 determine whether a reference position (forexample, upper left corner) of the current block in a reference pictureis included in motion estimation region 1050 determined temporarily. Forexample, in FIG. 21 , region determiners 1262 and 2182 determine whethermotion estimation region 1050 temporarily determined includes position1051 corresponding to a zero motion vector.

Here, when the position corresponding to the zero motion vector is notincluded in the temporarily determined motion estimation region, regiondeterminers 1262 and 2182 correct the position of the temporarilydetermined motion estimation region so that the motion estimation regionincludes the position corresponding to the zero motion vector. Forexample, in FIG. 21 , motion estimation region 1050 temporarilydetermined does not include position 1051 corresponding to the zeromotion vector, and thus region determiners 1262 and 2182 correct motionestimation region 1050 to motion estimation region 1052. As a result,position 1051 corresponding to the zero motion vector is included incorrected motion estimation region 1052.

On the other hand, when the position corresponding to the zero motionvector is included in the temporarily determined motion estimationregion, region determiners 1262 and 2182 determine the temporarilydetermined motion estimation region as the motion estimation region asit is. Specifically, region determiners 1262 and 2182 do not correct theposition of the motion estimation region.

As described above, region determiners 1262 and 2182 according to thisvariation can determine a region suitable for the search of a motionvector for a current block as the motion estimation region, thusimproving the accuracy of the motion vector.

Variation 6 of Embodiment 1

Next, Variation 6 of Embodiment 1 is to be described. In Variation 5above, the position of the motion estimation region is corrected so thatthe position corresponding to the zero motion vector is included,whereas in this variation, the position of the motion estimation regionis corrected so that the position corresponding to the motion vector ofone neighboring block among a plurality of neighboring blocks isincluded.

The following describes this variation with reference to FIG. 22 . FIG.22 illustrates an example of a motion estimation region in Variation 6of Embodiment 1.

First, region determiners 1262 and 2182 temporarily determine a motionestimation region, based on, for example, an average motion vector,similarly to Variation 5. For example, region determiners 1262 and 2182temporarily determine motion estimation region 1050, as illustrated inFIG. 22 .

Here, region determiners 1262 and 2182 determine whether the positioncorresponding to the motion vector of one neighboring block among aplurality of neighboring blocks is included in the temporarilydetermined motion estimation region. For example, in FIG. 22 , regiondeterminers 1262 and 2182 determine whether motion estimation region1050 temporarily determined includes position 1053 corresponding tomotion vector 1011 of neighboring block 1001. A predeterminedneighboring block may be used as the one neighboring block among theneighboring blocks, and a left neighboring block or an upper neighboringblock may be used, for example.

Here, when the position corresponding to the motion vector of oneneighboring block among the neighboring blocks is not included in thetemporarily determined motion estimation region, region determiners 1262and 2182 correct the position of the temporarily determined motionestimation region so that the motion estimation region includes theposition corresponding to the motion vector of the one neighboringblock. For example, in FIG. 22 , motion estimation region 1050temporarily determined does not include position 1053 corresponding tomotion vector 1011 of neighboring block 1001, and thus regiondeterminers 1262 and 2182 correct motion estimation region 1050 tomotion estimation region 1054. As a result, position 1053 is included incorrected motion estimation region 1054.

On the other hand, when the position corresponding to the motion vectorof one neighboring block among the neighboring blocks is included in thetemporarily determined motion estimation region, region determiners 1262and 2182 determine the temporarily determined motion estimation regionas a motion estimation region as it is. Specifically, region determiners1262 and 2182 do not correct the position of the motion estimationregion.

As described above, region determiners 1262 and 2182 according to thisvariation can determine a region suitable for the search of a motionvector for a current block as a motion estimation region, and thus theaccuracy of the motion vector can be improved.

Variation 7 of embodiment 1

Next, Variation 7 of Embodiment 1 is to be described. In this variation,information on a motion estimation region is not included in abitstream, which differs from Embodiment 1 above. The followingdescribes this variation with reference to FIG. 23 , focusing on a pointdifferent from Embodiment 1 above.

FIG. 23 is a block diagram illustrating the functional configuration ofencoding and decoding system 300 according to Variation 7 ofEmbodiment 1. As illustrated in FIG. 23 , encoding and decoding system300 includes encoding system 310 and decoding system 320.

Encoding system 310 encodes an input video, and outputs a bitstream.Encoding system 310 includes communication device 311, encoder 312, andoutput buffer 313.

Communication device 311 exchanges capability information with decodingsystem 320 via, for instance, a communication network (not illustrated),and generates motion estimation region information based on thecapability information. Specifically, communication device 311 transmitsencoding capability information to decoding system 320, and receivesdecoding capability information from decoding system 320. Encodingcapability information includes information on throughput and a memorybandwidth for motion estimation in encoding system 310, for instance.Decoding capability information includes information on throughput and amemory bandwidth for motion estimation in decoding system 320, forinstance.

Encoder 312 encodes an input video, and outputs a bitstream to outputbuffer 313. At this time, encoder 312 performs substantially the sameprocessing as that performed by encoder 100 according to Embodiment 1,except that the size of a motion estimation region is determined basedon motion estimation region information obtained from communicationdevice 311.

Output buffer 313 is a so-called buffer memory, temporarily stores abitstream input from encoder 312, and outputs the stored bitstream todecoding system 320 via the communication network, for instance.

Decoding system 320 decodes the bitstream input from encoding system310, and outputs an output video to a display (not illustrated), forinstance. Decoding system 320 includes communication device 321, decoder322, and input buffer 323.

Similarly to communication device 311 of encoding system 310,communication device 321 exchanges capability information with encodingsystem 310 via a communication network, for instance, and generatesmotion estimation region information based on the capabilityinformation. Specifically, communication device 311 transmits decodingcapability information to encoding system 310, and receives encodingcapability information from encoding system 310.

Decoder 322 decodes the bitstream input from input buffer 323, andoutputs an output video to a display, for instance. At this time,decoder 322 performs substantially the same processing as that performedby decoder 200 according to Embodiment 1, except that the motionestimation region is determined based on the motion estimation regioninformation obtained from communication device 321. Note that if themotion estimation region determined based on the motion estimationregion information obtained from communication device 321 exceeds amotion estimation region processable by decoder 322, a messageindicating that decoding is impossible may be transmitted tocommunication device 321.

Input buffer 323 is a so-called buffer memory, temporarily stores abitstream input from encoding system 310, and outputs the storedbitstream to decoder 322.

As described above, according to encoding decoding system 300 accordingto this variation, even if information on a motion estimation region isnot included in a bitstream, encoder 312 and decoder 322 can performmotion estimation using the same motion estimation region. Accordingly,the encoding amount for a motion estimation region can be reduced. Inaddition, it is not necessary for region determiner 1262 to performprocessing for determining the horizontal pixel count and the verticalpixel count that indicate the size of the motion estimation region, andthus the amount of processing can be reduced.

Variation 8 of Embodiment 1

Note that in Embodiment 1 above, all reference pictures included in thereference picture list are sequentially selected, yet not necessarilyall the reference pictures need to be selected. This variation describesan example of limiting the number of selected reference pictures.

As with the case of determining the size of the motion estimationregion, region determiner 1262 of encoder 100 according to thisvariation determines the number of reference pictures permitted to beused in motion estimation in the FRUC mode (hereinafter, referred to asa permitted reference picture count), based on a memory bandwidth andthe throughput, for instance. Information on the determined permittedreference picture count (hereinafter, referred to as permitted referencepicture count information) is written into a bitstream.

Region determiner 2182 of decoder 200 according to this variationdetermines a permitted reference picture count based on the permittedreference picture count information parsed from the bitstream.

Note that the position in the bitstream where permitted referencepicture count information is written is not limited in particular. Forexample, similarly to the motion estimation region informationillustrated in FIG. 12 , permitted reference picture count informationmay be written in a VPS, an SPS, a PPS, a slice header, or a videosystem setting parameter.

The number of reference pictures used in the FRUC mode is limited basedon the permitted reference picture count determined in this manner.Specifically, region determiners 1262 and 2182 determine whether thereis an unselected reference picture and furthermore, the number ofselected reference pictures is less than the permitted reference picturecount, in step S111 in FIG. 13 , for example. Here, when there is nounselected reference picture or the number of selected referencepictures is greater than or equal to the permitted reference picturecount (Yes in S111), the processing proceeds to step S112. Accordingly,this prohibits selection of a reference picture from the referencepicture list which results in the excess of the permitted referencepicture count.

In this case, in step S111 in FIG. 13 , region determiners 1262 and 2182may select a reference picture in the ascending order of referencepicture index values or in the order of reference pictures temporallycloser to the current picture, for example. In this case, a referencepicture having a small reference picture index value or a referencepicture temporally close to the current picture is preferentiallyselected from the reference picture list. Note that the temporaldistance between the current picture and a reference picture may bedetermined based on the picture order count (POC).

As described above, region determiners 1262 and 2182 according to thisvariation can limit the number of reference pictures used in motionestimation to the number less than or equal to the permitted referencepicture count. Accordingly, the processing load for motion estimationcan be reduced.

Note that, for example, when time scalable encoding/decoding areperformed, region determiners 1262 and 2182 may limit the number ofreference pictures included in a lower hierarchy than the hierarchy ofthe current picture indicated by a time identifier, based on thepermitted reference picture count.

Variation 9 of Embodiment 1

Next, Variation 9 of Embodiment 1 is to be described. This variationdescribes a method of determining the size of the motion estimationregion when a plurality of reference pictures are referred to in interprediction.

When a plurality of reference pictures are referred to in interprediction, the size of the motion estimation region may depend on thenumber of reference pictures that are referred to in inter prediction,in addition to the memory bandwidth and the throughput. Specifically,region determiners 1262 and 2182 first determine the total size of aplurality of motion estimation regions in the plurality of referencepictures referred to in inter prediction, based on the memory bandwidthand the throughput. Then, region determiners 1262 and 2182 determine thesize of a motion estimation region in each reference picture, based onthe number of reference pictures and the determined total size.Specifically, region determiner 1262 determines the sizes of the motionestimation regions in the reference pictures so that the total of thesizes of the motion estimation regions in the reference pictures matchesthe total size of motion estimation regions determined based on thememory bandwidth and the throughput.

The motion estimation regions in reference pictures determined in thismanner is to be specifically described with reference to FIG. 24 . FIG.24 illustrates a motion estimation region in Variation 9 ofEmbodiment 1. In FIG. 24 , (a) illustrates examples of motion estimationregions in prediction in which two reference pictures are referred to(bi-prediction), and (b) illustrates examples of motion estimationregions in the prediction in which four reference pictures are referredto.

In (a) of FIG. 24 , motion estimation regions F20 and B20 are determinedfor forward reference picture 0 and backward reference picture 0,respectively. Pattern matching (template matching or bilateral matching)is performed in motion estimation region F20 and motion estimationregion B20.

In (b) of FIG. 24 , motion estimation regions F40, F41, B40, and B41 aredetermined for forward reference picture 0, forward reference picture 1,backward reference picture 0, and backward reference picture 1,respectively. Accordingly, pattern matching is performed within motionestimation regions F40, F41, B40, and B41.

Here, the total of the sizes of motion estimation regions F20 and B20substantially matches the total of the sizes of motion estimationregions F40, F41, B40, and B41. Specifically, the sizes of motionestimation regions in reference pictures are determined based on thenumber of reference pictures referred to in inter prediction.

As described above, region determiners 1262 and 2182 according to thisvariation can determine the sizes of motion estimation regions inreference pictures based on the number of reference pictures referred toin inter prediction. Accordingly, the total size of regions in whichmotion estimation is performed can be controlled, and thus processingload and the required amount of the memory bandwidth can be moreefficiently reduced.

Variation 10 of Embodiment 1

Next, Variation 10 of Embodiment 1 will be described. In this variation,the case of performing motion compensation prediction by bi-directionaloptical flow (BIO) and/or overlapped block motion compensation (OBMC),as required, following motion estimation and motion compensation in theFRUC mode (hereinafter referred to as FRUC processing) according toEmbodiment 1 and the respective variations thereof will be described indetail with reference to FIG. 25 and FIG. 26 . The FRUC mode is a modethat allows a motion vector to be determined without having to writeinformation regarding the motion vector in a stream, by performing costevaluation using a decoded picture or decoded block on the decoder side.Specifically, in the FRUC mode, the motion vector of a current block tobe coded/decoded is estimated without using the image of the currentblock to be coded/decoded. BIO processing and OBMC processing are eachan example of a correction process of correcting the motion vector orthe motion compensation image obtained in the FRUC mode.

FIG. 25 is a block diagram illustrating an internal configuration ofinter predictor 400 of an encoder/decoder according to Variation 10 ofEmbodiment 1. Inter predictor 400 according to this variation performsthe motion compensation prediction of each of FRUC, BIO, and OBMC. Asillustrated in FIG. 25 , inter predictor 400 includes region determiner401, obtained reference image manager 402, FRUC motion compensationpredictor 403, BIO motion compensation predictor 404, and OBMC motioncompensation predictor 405.

Region determiner 401 determines a motion estimation region in the samemanner as in Embodiment 1 or any of the variations thereof. In addition,region determiner 401 may determine, as the motion compensation region,a region inside a reference picture to be used in motion compensation.

Obtained reference image manager 402 holds, as information regarding aregion of a reference image, information regarding the motion estimationregion and/or the motion compensation region determined by regiondeterminer 401.

FRUC motion compensation predictor 403 obtains a reference image from aframe memory outside the encoder/decoder, and performs motion estimationusing the reference image and an input image (current image).Furthermore, FRUC motion compensation predictor 403 obtains a referenceimage from a frame memory outside the encoder/decoder, and performsmotion compensation using the reference image. At this time, the motionestimation region and the motion compensation region in the FRUC modeare limited according to the memory bandwidth between theencoder/decoder and the frame memory and the motion estimation or motioncompensation throughput of FRUC motion compensation predictor 403. Here,the motion estimation region and the motion compensation region in theFRUC mode (i.e., the first region) are limited to within the motionestimation region and the motion compensation region determined byregion determiner 401.

BIO motion compensation predictor 404 determines whether BIO processingis to be performed, based on the information regarding the region of thereference image obtained from obtained reference image manager 402. Inthe same manner, OBMC motion compensation predictor 405 determineswhether OBMC processing is to be performed, based on the informationregarding the region of the reference image obtained from obtainedreference image manager 402.

Note that when there is no limitation on the motion estimation regionand/or motion compensation region in the FRUC mode, inter predictor 400need not include region determiner 401. At this time, obtained referenceimage manager 402 may hold information regarding the regions of all thereference images obtained by FRUC motion compensation predictor 403. Inaddition, BIO motion compensation predictor 404 and OBMC motioncompensation predictor 405 may determine whether BIO processing and OBMCprocessing is to be performed, based on the information regarding theregions of all the reference images.

Next, processing performed by inter predictor 400 according to thisvariation will be described with reference to FIG. 26 . FIG. 26 is aflowchart illustrating processing performed by inter predictor 400 ofthe encoder and the decoder according to Variation 10 of Embodiment 1.

In FIG. 26 , processing is performed in the order of FRUC processing(S400), BIO processing (S500), and OBMC processing (S600). FRUCprocessing is the same as in Embodiment 1 or any of the variationsthereof.

In FRUC processing, first, region determiner 401 obtains informationlimiting the motion estimation region (S401). Specifically, regiondeterminer 401 determines, as the motion estimation region, a partialregion inside a reference picture for which motion estimation isallowed.

Next, FRUC motion compensation predictor 403 performs a block-based loopprocess (S402 to S408). In the block-based loop process, first, FRUCmotion compensation predictor 403 generates a candidate MV list (S403).Then, FRUC motion compensation predictor 403 excludes a candidate havinga motion vector corresponding to a position outside the limited motionestimation region, from candidates in the candidate MV list (S404). FRUCmotion compensation predictor 403 performs cost evaluation of theremaining candidates (S405), and selects the candidate with the lowestcost (S406). Lastly, FRUC motion compensation predictor 403 searches thevicinity of a position within the reference picture, which correspondsto the motion vector of the selected candidate (S407).

After the FRUC processing (S400), BIO processing (S500) is performed. Inthe BIO processing, first, BIO motion compensation predictor 404identifies a reference region required in BIO (S501). Specifically, BIOmotion compensation predictor 404 identifies, as the reference region, aregion inside a reference picture to be referred to in BIO. Thereference region identified here is an example of a second region.

BIO motion compensation predictor 404 determines whether the identifiedreference region (i.e., the second region) is entirely included in thereference image (i.e., the first region) obtained in the FRUC processing(S502). For example, BIO motion compensation predictor 404 determineswhether the entirety of the identified reference region is includedwithin the motion estimation region determined in step S401.

Here, when the identified reference region is entirely included in thereference image obtained in the FRUC processing (Yes in S502), asubblock-based loop process is performed (S503 to S505). In thesubblock-based loop process, motion compensation prediction by BIO isperformed (S504). On the other hand, when the identified referenceregion is not entirely included in the reference image obtained in theFRUC processing (No in S502), the subblock-based loop process isskipped.

After the BIO processing (S500), OBMC processing (S600) is performed. Inthe OBMC processing, a subblock-based loop process (S601 to S605) isperformed. In the subblock-based loop process, OBMC motion compensationpredictor 405 first identifies a reference region required in OBMC(S602). Specifically, OBMC motion compensation predictor 405 identifies,as the reference region, a region inside a reference picture to bereferred to in OBMC. The reference region identified here is an exampleof a second region.

OBMC motion compensation predictor 405 determines whether the identifiedreference region (i.e., the second region) is entirely included in thereference image (i.e., the first region) obtained in the FRUC processing(S603). For example, OBMC motion compensation predictor 405 determineswhether the entirety of the identified reference region is includedwithin the motion estimation region determined in step S401.

Here, when the identified reference region is entirely included in thereference image obtained in the FRUC processing (Yes in S603), motioncompensation prediction by OBMC is performed (S604). On the other hand,when the identified reference region is not entirely included in thereference image obtained in the FRUC processing (No in S603), thesubblock-based loop process is broken and the OBMC processing ends.

In this manner, in the example in the figure, following FRUC processing,BIO processing and OBMC processing are performed. At this time, when atleast part of the pixel region referred to in the BIO processing or theOBMC processing is outside the region of the reference image obtained inthe FRUC processing, the BIO processing or the OBMC processing thatrefers to the at least part of the pixel region is excluded from acandidate for which BIO processing or OBMC processing is to beperformed.

Furthermore, when, upon identifying a reference region required in eachof the BIO processing of the current block and the OBMC processing ofthe current subblock, it is determined that at least part of theidentified reference region is outside the region of the reference imageobtained in the FRUC processing, the BIO processing of the current blockand/or the OBMC processing of the current subblock may be prohibited.

Note that it is acceptable for only one of the BIO processing and theOBMC processing to be prohibited based on the reference region.

As described above, according to this variation, in inter motioncompensation prediction (for example, BIO, OBMC, etc.) following FRUCprocessing, the inter motion compensation prediction can be prohibitedwhen a region exceeding the reference image region obtained in the FRUCprocessing is to be referred to. Specifically, BIO processing or OBMCprocessing is permitted if the second region to be referred to in theBIO processing or the OBMC processing is entirely included in the firstregion to be referred to in the FRUC processing, otherwise, the BIOprocessing or the OBMC processing is prohibited. According to this, theincrease of external memory access associated with BIO processing andOBMC processing can be inhibited.

Note that a coded stream that is limited so that a region exceeding thereference image region obtained in the FRUC processing is not referredto may be decoded.

Note that in this variation the motion estimation region is limited inthe FRUC processing, yet the present disclosure is not limited to this.For example, in FRUC processing, the motion estimation region need notbe limited. In this case, since there is no need to obtain a newreference image in the inter motion compensation prediction (forexample, BIO, OBMC, etc.) following FRUC processing, external memoryaccess associated with the inter motion compensation predictionfollowing FRUC processing can be inhibited.

Other Variations of Embodiment 1

The above has given a description of an encoder and a decoder accordingto one or more aspects of the present disclosure, based on theembodiment and the variations, yet the present disclosure is not limitedto the embodiment and the variations. The one or more aspects of thepresent disclosure may also encompass various modifications that may beconceived by those skilled in the art to the embodiment and thevariations, and embodiments achieved by combining elements in differentembodiments, without departing from the scope of the present disclosure.

For example, in the embodiment and the variations described above,motion estimation in the FRUC mode is performed per block unit having avariable size called a coding unit (CU), a prediction unit (PU), or atransform unit (TU), but the present disclosure is not limited to this.Motion estimation in the FRUC mode may be performed per subblockobtained by further splitting a block having a variable size. In thiscase, a vector (for example, a mean vector or a median vector) fordetermining the position of the motion estimation region may be obtainedper picture, block, or subblock.

For example, in the embodiment and the variations described above, thesize of the motion estimation region is determined based on thethroughput and the memory bandwidth, for instance, yet the presentdisclosure is not limited to this. For example, the size of the motionestimation region may be determined based on the type of a referencepicture. For example, when a reference picture is a B picture, regiondeterminer 1262 determines the size of the motion estimation region tobe a first size, and when the reference picture is a P picture,determines the size of a motion estimation region to be a second sizelarger than the first size.

For example, in the embodiment and the variations described above, whenthe position corresponding to the motion vector that a candidate has isnot included in the motion estimation region, the candidate is excludedfrom the candidate list, but the present disclosure is not limited tothis. For example, when a portion or the entirety of an adjacent regioncorresponding to a motion vector that a candidate has is not included ina motion estimation region, the candidate may be excluded from thecandidate list.

For example, in the embodiment and the variations described above,pattern matching is performed within an adjacent region corresponding toa motion vector that the selected candidate has, yet the presentdisclosure is not limited to this. For example, pattern matching may notbe performed in an adjacent region. In this case, the motion vector thatthe candidate has may be determined as a motion vector for the currentblock as it is.

For example, in the embodiment and the variations described above, acandidate excluded from the candidate list has a motion vectorcorresponding to the position outside the motion estimation region, yetthe present disclosure is not limited to this. For example, if a pixelused for interpolation is not included in a motion estimation regionwhen motion compensation is performed with decimal pixel accuracy usinga motion vector that a candidate has, the candidate may be excluded fromthe candidate list. Specifically, whether a candidate is excluded may bedetermined based on the position of a pixel used to interpolate adecimal pixel. For example, when BIO or OBMC is applied, a candidate forwhich a pixel outside the motion estimation region is used in the BIO orOBMC may be excluded from the candidate list. For example, a candidatehaving the smallest reference picture index out of a plurality ofcandidates may be retained, and the other candidates may be excluded.

For example, the embodiment and the variations above have described thecase where a mode for limiting a motion estimation region in a referencepicture is applied at all times, yet the present disclosure is notlimited thereto. For example, whether the mode is applied or not may beselected per video, sequence, picture, slice, or block. In this case,flag information indicating whether the mode is applied may be includedin a bitstream. The position of the flag information in the bitstreamdoes not need to be limited in particular. For example, flag informationmay be included in the same position as that of the motion estimationregion information illustrated in FIG. 12 .

For example, the embodiment and the variations above have not describedin detail scaling of a motion vector, yet the motion vector of eachcandidate may be scaled, based on a reference picture serving as abasis, for example. Specifically, the motion vector of each candidatemay be scaled based on a reference picture having a reference pictureindex different from the reference picture index indicated by the resultof encoding/decoding. As the reference picture serving as a basis, forexample, a reference picture having a reference picture index “0” may beused. For example, as a reference picture serving as a basis, areference picture closest to the current picture in the output order maybe used.

Note that a motion estimation region may be limited similarly to theembodiment and the variations above also when a region in a positionabove the current block or shifted to the left of the current block in acurrent picture may be referred to, and the same block as the currentblock is searched for (for example, in the case of intra block copy),which differs from the case of inter frame prediction as in theembodiment and the variations described above.

Note that in the embodiment and the variations described above,information that defines association between the feature quantity or thetype of a current block or a current picture and the sizes of motionestimation regions may be predetermined, and with reference to theinformation, the size of the motion estimation region corresponding tothe feature quantity or the type of a current block or a current picturemay be determined. As the feature quantity, the size (pixel count) maybe used, for example, and as the type, a prediction mode (for example,single prediction or bi-prediction) may be used, for example.

Note that, in the foregoing embodiment and each of the variationsthereof, the motion estimation region that is limited in the FRUCprocessing may be determined by adding adjacent pixels to be referred toin the inter motion compensation prediction (for example, BIO, OBMC,etc.) following the FRUC processing. For example, the motion estimationregion in the FRUC processing may be determined to include the referenceregion to be referred to in the inter motion compensation prediction tobe performed after the FRUC processing. Specifically, in the same manneras in the foregoing embodiment and any of the variations thereof, it isacceptable to determine a motion estimation region that is limited toinclude a motion estimation region determined based on a motion vectorand a region that may be referred to in the inter motion compensationprediction following the FRUC processing.

Note that the motion estimation region may be determined to include thereference region to be referred to in LIC processing.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder.

Other configurations included in the system may be modified on acase-by-case basis.

[Usage Examples]

FIG. 25 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times.

In the event of, for example, some kind of an error or a change inconnectivity due to, for example, a spike in traffic, it is possible tostream data stably at high speeds since it is possible to avoid affectedparts of the network by, for example, dividing the processing between aplurality of edge servers or switching the streaming duties to adifferent edge server, and continuing streaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convert11.264 to 11.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 26 , that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 26 . Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 27 , metadata is storedusing a data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 28 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 29 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 28 and FIG. 29 , a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

[Other Usage Examples]

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 30 illustrates smartphone ex115. FIG. 31 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a television receiver, a digitalvideo recorder, a car navigation system, a mobile phone, a digitalcamera, or a digital video camera, for example.

The invention claimed is:
 1. An encoding method for encoding a pictureto generate a coded stream, the encoding method comprising: generating afirst prediction image of a current block included in a current pictureby referring to a first region included in a reference picture differentfrom the current picture; operating a bi-directional optical flowprocess to generate a second prediction image based on the firstprediction image by referring to a second region included in the firstregion, and not operating the bi-directional optical flow process byreferring to a third region not included in the first region; andencoding the current block based on the second prediction image.
 2. Adecoding method for decoding a coded stream to generate a picture, thedecoding method comprising: generating a first prediction image of acurrent block included in a current picture by referring to a firstregion included in a reference picture different from the currentpicture; operating a bi-directional optical flow process to generate asecond prediction image based on the first prediction image by referringto a second region included in the first region, and not operating thebi-directional optical flow process by referring to a third region notincluded in the first region; and decoding the current block based onthe second prediction image.